Advanced POWER Virtualization on IBM System p5 - Previous ...

Virtual Ethernet adapter creation
Partitions that communicate through virtual Ethernet have additional in-memory
channels implemented in the Hypervisor:
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The creation of in-memory channels between partitions occurs automatically
when configuring virtual Ethernet adapters for partitions on the HMC or IVM.
The AIX 5L or Linux kernel automatically creates a virtual network device for
each memory channel indicated by the <strong>POWER</strong>5 firmware.
The AIX 5L configuration manager creates the necessary ODM objects for
the:
– Ethernet network adapter device (ent*) with available state
– Ethernet network interface device (en* and et*) with defined state
A unique 6 byte Media Access Control (MAC) address (also called Ethernet,
hardware or layer-2 address) is generated when the virtual Ethernet device is
created on the HMC or IVM. A prefix value can be assigned for the system so
that the auto-generated MAC addresses in a system consist of a common
system prefix, plus an algorithmically-generated unique part per adapter. Thus,
the generated MAC addresses will not conflict with those of other network
devices.
The virtual Ethernet can also be used as a bootable device to allow such tasks
as operating system installations to be performed using NIM.
Dynamic partitioning for virtual Ethernet devices
Virtual Ethernet resources can be assigned and removed dynamically through
dynamic LPAR-operations. On the HMC or IVM, virtual Ethernet target and
server adapters can be assigned and removed from a partition using dynamic
logical partitioning. The creation of physical and virtual Ethernet adapters on the
Virtual I/O Server can also be done dynamically. After the addition of an adapter
on the HMC, be it virtual or physical, the cfgmgr command has to be run in an
AIX 5L partition, and the cfgdev command on the Virtual I/O Server.
4.1.6 Performance considerations for Virtual I/O Servers
The transmission speed of virtual Ethernet adapters is in the range of multiple
gigabits per second, depending on the transmission size (MTU) and overall
system performance. Virtual Ethernet connections generally take up more CPU
cycles than connections through physical Ethernet adapters. The reason is that
modern physical Ethernet adapters contain many functions to off-load some work
from the system’s CPUs, for example, checksum computation and verification,
interrupt modulation, and packet reassembly. These adapters use Direct Memory
Access (DMA) for transfers between the adapter and the RAM, which uses only a
Chapter 4. Setting up virtual I/O: advanced 203